Name: Applications of TIR: Mirage and Looming
Uploaded: 2019-07-19
Duration: 4 min 7 s
Description: Let’s learn about mirages and looming in this interesting video. These are fascinating phenomena of light observed on hot summer days.

Question

Explain the refraction of light, write its laws and also write the basic cause of refraction of light. Derive the relation $n = \frac{Real depth}{Apparent depth}$ .

Accepted Answer

The light travels in different media at different speeds. Its speed is highest in air or vacuum. Hence, when it travels from one medium into another, it deviates from its original path. The angle $(i)$ made with the normal at the surface in the first medium is different from the angle $(r)$ in the second medium.

Two laws were given by Snell for the phenomenon of refraction:

(i) The incident ray, the refracted ray and the normal to the interface at the point of incidence, all lie in the same plane.

(ii) The ratio of the sine of the angle of incidence $(i)$ to the sine of the angle of refraction $(r)$ is constant.

$\frac{\sin i}{\sin r} = n_{21}$

Where $n_{21}$ is the refractive index of the second medium with respect to the first medium.

Light travels with different velocity in different media. This is the reason behind its bending away or bending towards the normal at the interface.

When an observer looks at a point in the denser medium from a rarer medium, the light rays falling on the retina of her eyes travels from a denser medium into a rarer medium. The ray diagram for the above said situation is shown below:

$Chapter 4 Refraction of Light at Plane Surfaces - Concise Physics Part II - Selina Solutions for Class 10 Physics ICSE - TopperLearning$

Let O be a point in the denser medium. The Light ray AO travels normally through the interface hence, it goes undeviated. The oblique ray OB will bend away from the normal as it enters into a rarer medium. It follows the path BC. Now I is the image of point O. Considering the $∠ i$ and $∠ r$ to be very small, in $∆ AOB$ and $△ AIB$ :

$\sin i = \tan i = \frac{A B}{A O}$ .......(i)

$\sin r = \tan r = \frac{A B}{A I}$ ......(ii)

The refractive index of the denser medium with respect to rarer medium:

$n = \frac{\sin r}{\sin i} = \frac{AO}{AI}$ .......(iii)

AO is the real depth of the object and AI is the distance of the image, hence:

$n = \frac{real depth}{apparent depth}$

Explain the refraction of light, write its laws and also write the basic cause of refraction of light. Derive the relation $n = \frac{Real depth}{Apparent depth}$ .

Important Questions on Refraction of Light at a Plane Interface : Total Internal Reflection : Optical Fibre

Learn and Prepare for any exam you want !

Explain the refraction of light, write its laws and also write the basic cause of refraction of light. Derive the relation n= Real depth Apparent depth .

Important Questions on Refraction of Light at a Plane Interface : Total Internal Reflection : Optical Fibre

Learn and Prepare for any exam you want !

Explain the refraction of light, write its laws and also write the basic cause of refraction of light. Derive the relation $n = \frac{Real depth}{Apparent depth}$ .